Illumination Light Source and 2-D Image Display Device Using the Same

ABSTRACT

In a laser display that displays a video by scanning a beam from a laser light source two-dimensionally on a screen, the image quality being displayed is deteriorated markedly by speckle noises induced from coherency of the light source. A method for oscillating the screen to remove the speckles has problems that a large-scale device is necessary and the screen cannot be chosen without any restrain. 
     A speckle pattern being generated is changed at a high speed by oscillating a light spot on the screen at a high speed using beam oscillation means  3 , so that the viewer acknowledges time-mean image having no speckle noises.

TECHNICAL FIELD

The present invention relates to an image display device using a laserlight source, such as a TV receiver and a video projection device, andto an illumination light source to project an image.

BACKGROUND ART

FIG. 7 is a view schematically showing the configuration of a laserdisplay in the related art described in detail, for example, inNon-Patent Document 1. Light beams from laser light sources for threecolors, RGB, are combined by dichroic mirrors 102 a and 102 b, andscanned in the horizontal direction by a polygon scanner 104 and in thevertical direction by a galvanometer scanner 105 to be irradiated onto ascreen 108. In this instance, a video is displayed on the screen bymodulating intensity by light modulators 106 a through 106 c accordingto an input video signal. For example, in order to display a movingimage corresponding to an NTSC video signal, about 500 scan lines in thehorizontal direction are displayed for 30 frames per second, and thenumber of horizontal scan lines in total is 15,000 per second. This canbe achieved by rotating a polygon scanner having 30 faces at 30,000 rpm.The galvanometer mirror is oscillated to reciprocate in the verticaldirection 30 times per second. The resolution in the horizontaldirection is determined by a modulation rate of the light modulatorswith respect to the scan rate. For example, in order to obtain theresolution comparable to 500 TV lines in the horizontal direction at thescan rate specified above, a bandwidth of about 10 MHz is necessary onthe basis of 500×15,000=7,500,000. Such a bandwidth can be achieved witha light modulator using the acousto-optic effect or a light modulatorusing the electro-optic effect.

The display configured in this manner is characterized in that it candisplay a sharp image having high color purity by using laser lightsources having adequate wavelengths because light beams from therespective light sources for RGB are monochromatic light. Sharp colordisplay of each monochromatic light can be achieved, for example, byusing a krypton ion laser having a wavelength of 647.1 nm as the redlight source, a helium-cadmium laser having a wavelength of 441.6 nm asthe blue light source, and a second harmonic of a neodymium-doped YAGlaser having a wavelength of 532 nm as the green light source.

The display configured as shown in FIG. 7, however, has a problem ofso-called speckle noises resulting from the use of a highly coherentlaser light source as the light source. The speckle noises aremicroscopic irregular noises induced by mutual interference of scatteredlight from the respective portions on the screen 108 as a laser beamscatters on the screen 108. The screen 108 has a random surface shape,and a laser beam scattered on the screen causes interference due to amicroscopic concavoconvex shape, and generates a microscopic bright-darkpattern depending on a viewing direction. This pattern results in thespeckle noises.

In the related art, the speckle noises are removed by oscillating thescreen 108. This technique uses the fact that the speckle patternchanges as the interference state on the screen varies from time to timebecause the position of the screen keeps changing. The speckles do notdisappear in every moment; however, the pattern changes at a high speeddue to oscillation, and the viewer acknowledges the resulting time-meanpattern. The viewer therefore views an image as if the speckles haddisappeared. The method of oscillating the screen as described above canindeed remove the speckles effectively from a viewed image; however,there is a need to use a special screen that can be oscillated. Thisraises a problem that a fixed wall surface, for example, cannot be usedas the screen without any restraint.

Non-Patent Document 1: Baker et al., “A large screen real-time displaytechnique”, Proc. Society for Information Display 6th Nati'l Symp.,85-101 (1965)

DISCLOSURE OF THE INVENTION

The invention therefore has an object to solve these problems andprovide an illumination light source capable of effectively suppressingspeckle noises specific to a case where a coherent light source, such asa laser light source, is used, and a 2-D image display device using thisillumination light source and capable of displaying a high-qualityvideo.

The above and other objects are achieved by a 2-D image display deviceaccording to one aspect of the invention, which includes: a coherentlight source; 2-D beam scan means for scanning light from the coherentlight source two-dimensionally; light intensity modulation means formodulating the light from the coherent light source in intensity; andbeam oscillation means for minutely oscillating the light from thecoherent light source.

According to this aspect, light from the coherent light source ismodulated in intensity by the light intensity modulation means accordingto, for example, an input video signal, and can be projected onto acertain wall or the like that functions as a screen. The projected lightis scanned on the screen two-dimensionally by the 2-D beam scan meanshaving a combination selected from, for example, a polygon scanner, agalvanometer scanner, etc. In this instance, the projected light isoscillated minutely by the beam oscillation means, and therebyirradiates different sites on the screen successively. The pattern ofthe speckle noises induced by scattered light therefore changes oneafter another as well. This allows the time-mean pattern of the specklenoises to be perceived by human eyes. It is thus possible to display ahigh-quality video in which the speckle noises specific to a deviceusing a coherent light source, such as a laser light source, can besuppressed effectively.

Also, an illumination light source according to another aspect of theinvention includes: a coherent light source; beam scan means forscanning light from the coherent light source; light intensitymodulation means for modulating the light from the coherent light sourcein intensity; and beam oscillation means for minutely oscillating thelight from the coherent light source.

According to this aspect, light from the coherent light source ismodulated in intensity by the light modulation means according to, forexample, an input video signal, and projected onto a certain screen orthe like. In this instance, the beam scan means can be configured toscan the light either one-dimensionally or two-dimensionally. In thecase of the configuration to scan the light one-dimensionally, byproviding a mechanism that scans light in a direction orthogonal to thescan direction to the outside, it is possible to display an image, forexample, on a 2-D screen.

Also, projected light is oscillated minutely by the beam oscillationmeans, and thereby irradiates different sites on the screensuccessively. The pattern of the speckle noises induced by scatteredlight therefore changes one after another as well. This allows thetime-mean pattern of the speckle noises to be perceived by human eyes.It is thus possible to achieve a light source capable of displaying ahigh-quality video in which the speckle noises specific to a deviceusing a coherent light source, such as a laser light source, can besuppressed effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing the configuration of a firstembodiment of a 2-D image display device of the invention;

FIG. 2 is a view showing a scan method of an illumination beam in thefirst embodiment of the 2-D image display device of the invention;

FIG. 3 is a view schematically showing beam oscillation means in thefirst embodiment of the 2-D image display device of the invention;

FIG. 4 is a view schematically showing a second embodiment of the 2-Dimage display device of the invention;

FIG. 5 is a view schematically showing one example in which wavelengthconversion means using a second harmonic generator device and beamoscillation means are integrated into the same substrate;

FIG. 6 is a view schematically showing the configuration of a thirdembodiment of the 2-D image display device of the invention; and

FIG. 7 is a view schematically showing the configuration of a laser 2-Dimage display device in the related art.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the invention will be described withreference to the drawings.

First Embodiment

FIG. 1 is a view schematically showing the configuration of a 2-D imagedisplay device of the invention. Light beams emitted from a red laserlight source 1 a, a green laser light source 1 b, and a blue laser lightsource 1 c are modulated, respectively, by light modulators 6 a, 6 b,and 6 c that modulate light according to a video signal, and thencombined by dichroic mirrors 2 a and 2 b. Further, a light beam isdeflected in the x-direction (horizontal scan) by a polygon scanner 4and subsequently deflected in the y-direction (vertical scan) by agalvanometer scanner 5 to be projected onto a screen 8 in the form of a2-D image. In this instance, light beams modulated by the lightmodulators 6 a through 6 c are oscillated minutely on the screen 8 bybeam oscillation means 3. In this instance, the beam on the screen iscollected by a light collection lens 9 to form a minute light spot. Thesize of the light spot is smaller than oscillation amplitude on thescreen 8 by the beam oscillation means 3.

In this embodiment and second and third embodiments below, a combinationselected from the polygon scanner 4 and the galvanometer scanner 5 isfurnished with a function of 2-D beam scan means, the light modulators 6a through 6 c are furnished with a function of light intensitymodulation means, and the light collection lens 9 is furnished with afunction of beam collection means.

An He—Ne laser and an AlGaInP-based semiconductor laser can be used asthe red laser light source 1 a. An Ar laser and an SHG laser using a YAGsolid-state laser as the fundamental harmonic can be used as the greenlaser light source 1 b. An He—Cd laser, a GaN-based semiconductor laser,and an SHG laser using a YVO4 solid-state laser as the fundamentalharmonic can be used as the blue laser light source 1 c.

A manner in which the speckle noises are suppressed will now bedescribed using a scan pattern of a light spot on the screen 8. FIG. 2is a view showing a manner in which a light spot is scanned on thescreen 8. Light coming incident on the screen 8 is scanned as indicatedby a dotted line by the polygon scanner 4 and the galvanometer scanner 5as has been described above, so that it irradiates a rectangular regioncovering the entire screen 8 while being modulated in intensityaccording to a pixel at the scan position.

The pixel on the screen referred to herein means a region having, as oneside in the longitudinal direction (vertical direction) of FIG. 2, alength equal to an interval between adjacent scan lines (in thisembodiment, in the horizontal direction) scanned by the polygon scanner4 and the galvanometer scanner 5, and having, as one side in the lateraldirection (horizontal direction), a length in the scan line directionthat is scanned by the polygon scanner 4 and the galvanometer scanner 5for a time during which data corresponding to one pixel in an inputvideo signal, which is a digital signal, is transmitted. In short, thepixel is defined herein by ignoring the light spot diameter.

Because a light spot is oscillated by the beam oscillation means 3 at aspeed higher than by the polygon scanner 4 and the galvanometer scanner5, it is oscillated at a high speed within a given pixel while thisparticular pixel is being displayed as is shown in FIG. 2. In thisinstance, minute concavity and convexity are present on the screen 8,and the light spot oscillates and thereby irradiates different sites inthe concavoconvex pattern as the beam is oscillated minutely. Thepattern of the speckle noises induced by scattering therefore changes aswell at a high speed in association with oscillation of the beam. Inother words, the speckle pattern viewed by the viewer while a givenpixel is being displayed changes at a high speed, and this allows thetime-mean speckle pattern to be perceived when the speckle patterns areviewed by human eyes. A video as if the speckle pattern had disappearedis thus acknowledged.

In order to suppress the speckles effectively, the speckles are changedat a higher speed while one pixel is displayed. This can be achieved byminutely oscillating a beam thoroughly and two-dimensionally within apixel while an input video signal for this particular pixel isdisplayed, so that the beam irradiates more concavoconvex patters on thescreen 8. However, by taking it into account that the respective pixelsare scanned successively by the polygon scanner 4 while an image isdisplayed, as is shown in the drawing, it is possible to oscillate andscan a beam within a pixel two-dimensionally at a high speed by minutelyoscillating the beam at a high speed one-dimensionally in a directionperpendicular to the scan direction of the polygon scanner 4. Whenconfigured in this manner, the beam oscillation means 3 only has tooscillate a beam in a one-dimensional direction. Oscillation can be thusachieved with a simple manipulation.

In order to suppress the speckles on the principle as above, a lightspot diameter on the screen 8 needs to be smaller than the oscillationamplitude of a beam, and the concavity and convexity on the screen 8that a light spot can sense need to change with oscillation of the beam.Also, it is necessary to prevent deterioration of image resolution bylimiting the oscillation amplitude of a beam to a range smaller than onepixel of the video.

FIG. 3 is a view showing one example of the beam oscillation means 3used in the 2-D image display device of the invention. According to theexample of the drawing, a triangular polarization inversion region 21 ais formed in an electro-optic crystal substrate 20 a for a light beam topass through. A refractive index of the electro-optic crystal substrate20 a varies when a voltage in the positive or negative direction of thez-axis is applied between a surface electrode 22 a and a backsideelectrode 23 a. In this instance, the refractive index of thepolarization inversion region 21 a varies inversely with respect to theother region within the electro-optic crystal substrate 20 a. Thepolarization inversion region 21 a therefore serves as a prism. Hence,assume that an incident direction of an incident beam 25 is the positivedirection of the y-axis, then an exiting beam 26 is refracted to aspecific one direction, which is either the positive or negativedirection of the x-axis. In addition, when the direction of a voltageapplied between the surface electrode 22 a and the backside electrode 23a is inverted, the refractive index varies inversely with respect to thechange above. The incident beam 25 is therefore refracted to a specificone direction, which is either the positive or negative direction of thex-axis and in a direction opposite to the direction refracted above.

In addition, by using an ac power supply 24 a as the power supply thatapplies a voltage, it is possible to vary the refractive index at a highspeed in response to the frequency of the ac power supply 24 a. It istherefore possible to oscillate the incident beam 25 at a high frequencyequivalent to the frequency of the ac power supply 24 a. Further, bychanging magnitude of an applied voltage, a refractive angle can bechanged correspondingly. It is therefore possible to oscillate a beam atdifferent oscillation angles. In short, when the ac power supply 24 a isused, it is possible to oscillate a beam in a specific one-dimensionaldirection continuously at a high speed.

In an experiment, lithium niobate crystal was used as the electro-opticcrystal, and the surface electrode 22 a and the backside electrode 23 awere formed by means of photolithography. The polarization inversionregion 21 a was formed by applying a voltage of 1 kV between these twoelectrodes. Both the crystal thickness and the polarization inversionregion width were 1 mm, and it was possible to deflect a beam as largeas 1 mm in diameter. For beam oscillation, a deflection angle (indicatedby θ in FIG. 3) of 0.2 degree was obtained on an applied voltage of 20V.

Also, the beam oscillation means 3 of FIG. 3 uses lithium niobatecrystal, which is an electro-optic crystal. However, this crystal isoften used also as a light wavelength conversion element due to its highnon-linear constant. The wavelength conversion technique is useful alsofor the 2-D image display device of the invention. For example, byallowing infrared light of 1064 nm to go incident thereon and light ofhalf the wavelength to exit therefrom, it is possible to obtain a greenlaser beam of 532 nm. In this instance, the number of components formingthe light source and the beam oscillation means can be reduced byintegrating the beam oscillation means 3 of FIG. 3 on the lithiumniobate crystal used for wavelength conversion as will be describedbelow. A laser light source using the wavelength conversion ischaracterized in that a light source more compact than a gas laser, suchas an argon laser used in the related art, can be achieved. Byexploiting such a characteristic, when a gallium nitride semiconductorlaser light source and an AlGaInP semiconductor laser light source areused as blue and red coherent light sources, respectively, a compact 2-Dimage display device can be achieved. In this case, the speckle noisescan be suppressed by integrating the beam oscillation means as describedabove. Also, because semiconductor laser light sources are used for redlight and blue light, the coherency of laser beams is reduced byapplying a high frequency current to an injection current for thesemiconductor laser light sources, which can in turn reduce thespeckles. By using the light source employing the wavelength conversionelement and the semiconductor laser light source, integrating the beamoscillation means in the light source employing the wavelengthconversion element, and applying a high frequency current to theinjection current for the semiconductor laser in this manner, it ispossible to reduce the overall device in size and reduce the number ofcomponents.

Of the optical systems shown in FIG. 1, a speckle evaluation opticalsystem is constructed using the green laser light source 1 b, the lightcollection lens 9, the beam oscillation means 3, the polygon scanner 4,the galvanometer scanner 5, and the screen 8, and suppression of thespeckles was confirmed by performing an experiment as follows. Thepolygon scanner was an 8-faced mirror driven at 10,000 rpm, and thegalvanometer scanner was driven on a triangular wave at 100 Hz. Adistance from the light collection lens to the screen 8 was 3 m. It wasconfirmed that when no voltage was applied to the beam oscillation means3, fine speckle noises were superimposed uniformly across an image,whereas the speckle patterns disappeared by applying a sine wave to thebeam oscillation means at 1 MHz on ±20 V. The size of light on thescreen 8 was about 100 μm, and the beam oscillation amplitude was about1 mm.

In this experiment, a light deflector using the electro-optic effect wasused as the beam oscillation means 3. However, a light deflector usingthe acousto-optic effect can be used as well. It should be noted,however, that because the light deflector using the acousto-optic effectdeflects light by means of the grating inside the crystal, it is able todeflect light having a specific wavelength alone. Hence, when the lightdeflector using the acousto-optic effect is used, one light deflector isnecessary for each color.

Second Embodiment

FIG. 4 is a view schematically showing the configuration of a secondembodiment of the 2-D image display device of the invention. The firstembodiment above is configured in such a manner that light beams emittedfrom the red laser light source 1 a, the green laser light source 1 b,and the blue laser light source 1 c are combined first, and thenoscillated by the beam oscillation means 3. Different from the aboveconfiguration, in this embodiment, an infrared coherent light source 33b and wavelength conversion means 32 b are used as a green light source,and green light alone is oscillated by beam oscillation means 3 b. Forexample, a YAG laser having a wavelength of 1064 nm is used as theinfrared coherent light source 33 b, and a second harmonic generatordevice, in which the lithium niobate substrate has a cyclic polarizationinversion structure, is used as the wavelength conversion means 32 b.The wavelength conversion means 32 b allows light having half thewavelength of light coming incident thereon, herein green light havingthe wavelength of 532 nm, to exit. As will be described below, both thewavelength conversion means 32 b and the beam oscillation means 3 b areformed on the same lithium niobate substrate.

The red laser light source 1 a is a semiconductor laser based onAlGaInP, and the blue laser light source 1 c is a semiconductor laserbased on GaN. High frequency currents from high frequency currentsuperimposing means 31 a and 31 c are applied to currents for drivingthese light sources. In this instance, because laser beams emitted fromthe red laser light source 1 a and the blue laser light source 1 cexpand in spectrum bandwidth, the coherency is reduced. As a result,speckle noises induced by scattering on the screen 8 can be suppressed.The high frequency current superimposing means 31 a and 31 c can beachieved by the method and the configuration same as those used normallyto reduce noises induced by return light of the semiconductor laserlight source that is used for an optical disc pick-up in the relatedart.

FIG. 5 is a view schematically showing the configuration of one examplein which wavelength conversions means using the second harmonicgenerator device and beam oscillation means are integrated into the samesubstrate. In the wavelength conversion means 32 b, the directions ofpolarization are inverted in a cycle along the traveling direction ofthe incident beam 25. This structure is referred to as the cyclicpolarization inversion structure. When coherent light comes incident onhomogeneous lithium niobate having no polarization inversion, the phasesof the second harmonics generated at respective portions in theelectro-optic crystal plate 20 a change due to wavelength dispersion.This makes highly efficient wavelength conversion impossible. On thecontrary, in the device shown in FIG. 5, the cyclic polarizationinversion structure compensates for wavelength dispersion of lithiumniobate, so that the second harmonics generated at the respectiveportions in the crystal are added up in-phase. Highly efficientwavelength conversion is thus enabled. The wavelength conversiontechnique is described in detail in Journal of Applied Physics, Vol. 96,2004, No. 11, 6865-6590.

A beam exiting from the wavelength conversion means 32 b is oscillatedin a one-dimensional direction by the adjacently integrated beamoscillation means 3 b (see FIG. 3). In this instance, too, a beam can beoscillated in a specific one-dimensional direction (the positive ornegative direction of the x-axis in FIG. 5) continuously at a high speedwith the use of the ac power supply 24 a as has been described withreference to FIG. 3.

As is shown in FIG. 5, by integrating the wavelength conversion means 32b and the beam oscillation means 3 b into the same substrate, the numberof components can be reduced. In addition, the cyclic polarizationinversion region 40 and the polarization inversion region 21 a in thebeam oscillation means 3 b can be formed by making electrodes of thesame shapes as the respective polarization inversion regions and byapplying a high voltage simultaneously. Hence, by integrating the beamoscillation means 3 b and the wavelength conversion means 32 b into thesame substrate as in this embodiment, the steps in the fabricationsequence of the device can be fewer. According to the configuration ofthe second embodiment as has been described, it is possible to achieve a2-D image display device capable of displaying a sharp color image inwhich the speckle noises are suppressed.

Third Embodiment

FIG. 6 is a view schematically showing a third embodiment of the 2-Dimage display device of the invention. In this embodiment, infraredcoherent light sources 33 b and 33 c and wavelength conversion means 32b and 32 c are used as light sources for green and blue, respectively,and green light and blue light are oscillated by beam oscillation means3 b and 3 c, respectively. The infrared coherent light source 33 b, thewavelength conversion means 32 b, and the beam oscillation means 3 b arethe same as their counterparts in the second embodiment above, and thedescription of these components is omitted herein.

For example, a semiconductor laser having a wavelength of 850 nm is usedas the infrared coherent light source 33 c, and a second harmonicgenerator device, in which the lithium niobate substrate has the cyclicpolarization inversion structure same as that in the wavelengthconversion means 32 b, is used as the wavelength conversion means 32 c.It should be noted, however, that polarization inversion cycles aredifferent in the wavelength conversion means 32 c for blue and in thewavelength conversion means 32 b for green. Blue light having awavelength of about 425 nm exits from the wavelength conversion means 32c.

Also, as was in the second embodiment above, the red laser light source1 a is a semiconductor laser based on AlGaInP, and a high frequencycurrent from the high frequency current superimposing means 31 a isapplied to a current driving this semiconductor laser. Processes afterbeams emitted from these coherent light sources are modulated by thelight modulators 6 a through 6 c are the same as those in the secondembodiment above, and the description of these processes is omittedherein. According to the configuration of the third embodiment as hasbeen described, it is possible to achieve a 2-D image display devicecapable of displaying a sharp color image in which the speckle noisesare suppressed.

While a color display device has been chiefly described, the inventionis also applicable to a monochromatic system, such as an aligner forintegrated circuit manufacturing. In this case, a glass mask, on whichan exposure pattern is formed, is used instead of the screen, andtransmitted light is further projected onto a semiconductor wafer usinga reduction projection lens.

In addition, while a front-projection type display has been described,it is obvious that the invention is also applicable to a rear-projectiontype display device, and an illumination optical system for a displaydevice of a type that a 2-D optical switch is illuminated from behindfor the viewer to view transmitted light, like a normal liquid crystaldisplay.

SUMMARY OF THE EMBODIMENTS

Hereinafter, the embodiments of the invention will be described briefly.

(1) As has been described, it is preferable that a 2-D image displaydevice according to the invention of the present application includes acoherent light source, 2-D beam scan means for scanning light from thecoherent light source two-dimensionally, light intensity modulationmeans for modulating the light from the coherent light source inintensity, and beam oscillation means for minutely oscillating the lightfrom the coherent light source.

According to this configuration, light from the coherent light source ismodulated in intensity by the light intensity modulation means accordingto, for example, an input video signal, and can be projected onto acertain wall or the like that functions as a screen. The projected lightis scanned on the screen two-dimensionally by the 2-D beam scan meanshaving a combination selected from, for example, a polygon scanner, agalvanometer scanner, etc. In this instance, the projected light isoscillated minutely by the beam oscillation means, and therebyirradiates different sites on the screen successively. The pattern ofthe speckle noises induced by scattered light therefore changes oneafter another as well. This allows the time-mean pattern of the specklenoises to be perceived by human eyes. It is thus possible to display ahigh-quality video in which are suppressed the speckle noises specificto a display device using a coherent light source, such as a laser lightsource.

(2) A 2-D image display device is the 2-D image display device set forthin (1), characterized by further including beam collection means forcollecting the light from the coherent light source onto a screen.According to this configuration, the beam collection means enables thelight from the coherent light source to be projected intact onto thescreen in the form of a small spot without causing any expansion. It isthus possible to prevent spots from overlapping one another even whenthe amplitude of oscillation by the beam oscillation means is reduced,which in turn enables a high-quality video having less blurring to bedisplayed. In addition, when configured in such a manner that the beamcollection means is able to control the spot diameter, the spot diametercan be controlled to match with the concavity and convexity on thescreen. The 2-D image display device can be therefore used forprojection onto various screens.

(3) A 2-D image display device is the 2-D image display device set forthin (1) or (2), wherein it is preferable that the beam oscillation meansoscillates the light from the coherent light source in a directionperpendicular to a scan line by the 2-D beam scan means.

According to this configuration, for example, regardless of whether ascan line scanned by the 2-D beam scan means is in the horizontaldirection or in the vertical direction, the beam oscillation meansoscillates the light from the coherent light source in a one-dimensionaldirection perpendicular to the scan direction. In other words, becausethe beam oscillation means only has to oscillate the light in aone-dimensional direction, oscillation can be achieved with a simpleconfiguration. Further, because the light is oscillated perpendicularlyto the scan line, the light can be scanned on a two-dimensional planeefficiently. It is thus possible to display a high-quality video havingno irregularities.

(4) A 2-D image display device is the 2-D image display device set forthin any of (1) through (3), wherein it is preferable that the beamoscillation means oscillates the light on the screen in amplitude equalto or larger than a spot diameter of the light collected on the screenby the beam collection means, and equal to or smaller than an intervalof scan lines by the 2-D beam scan means.

According to this configuration, the beam oscillation means oscillatesthe light in amplitude equal to or larger than the spot diameter of thelight collected on the screen. The collected light therefore irradiatesdifferent sites on the screen successively without overlapping oneanother. It is thus possible to display a high-quality video in whichthe speckle noises are suppressed effectively. Further, because theamplitude in which the collected light is oscillated is equal to orsmaller than the interval of the scan lines, overlapping of videosprojected on the adjacent scan lines can be controlled to be small. Itis thus possible to display a high-quality video having less blurring.

(5) A 2-D image display device is the 2-D image display device set forthin any of (1) through (4), wherein it is preferable that while the 2-Dbeam scan means scans the light from the coherent light sourcecomparable to one digital image data along a scan line, the beamoscillation means oscillates the light at least from largest amplitudeto following largest amplitude.

Digital image data referred to herein means data corresponding to onepixel in an input video signal, which is a digital signal. Hence, adistance over which light corresponding to one digital image data isscanned along the scan line by the 2-D beam scan means corresponds tothe size of the pixel on the screen in the scan line direction. In otherwords, the beam oscillation means oscillates the light at least from thelargest amplitude to the following largest amplitude while the 2-D beamscan means scans the light over the distance comparable to one pixel onthe screen. For example, assume that the scan line is in the horizontaldirection, then the above description means that the light is oscillatedfrom the highest position to the lowest position in the verticaldirection in a given pixel during oscillation along the scan line, andthe light is subsequently oscillated from the lowest position to thehighest position in the vertical direction in the next adjacent pixel.It is preferable that the beam oscillation means oscillates the light alarger number of times while the 2-D beam scan means scans the lightover the distance comparable to one pixel on the screen. As a result,the 2-D beam scan means is able to scan the light on a two-dimensionalplane efficiently while suppressing the speckle noises. It is thuspossible to display a high-quality video having no irregularities.

(6) A 2-D image display device is the 2-D image display device set forthin any of (1) through (5), wherein it is preferable that while the 2-Dbeam scan means scans the light from the coherent light sourcecomparable to one digital image data along a scan line, the beamoscillation means oscillates the light in an non-integral multiple ofone cycle.

When the beam oscillation means oscillates the light in an integralmultiple of one cycle, such as one cycle or two cycles, while the 2-Dbeam scan means scans the light corresponding to one digital image data,there is a possibility of the occurrence of moire, which is a cyclicbanded pattern. However, more will not occur when the beam oscillationmeans oscillates the light in a non-integral multiple of one cycle, suchas 1.8 cycles. It is thus possible to display a high-quality video.

(7) A 2-D image display device is the 2-D image display device set forthin any of (1) through (5), wherein it is preferable that in a case wherethe light from the coherent light source is oscillated in N cycles bythe beam oscillation means while the 2-D beam scan means scans the lightfrom the coherent light source comparable to one digital image dataalong a scan line, a spot diameter of the light projected onto thescreen is of a size equal to or larger than 1/(4N) of a distance overwhich the light is scanned by the 2-D beam scan means within the scantime.

According to this configuration, a two-dimensional plane can be fullyfilled out with light spots. It is thus possible to display ahigh-quality video having no irregularities.

(8) A 2-D image display is the 2-D image display device set forth in anyof (1) through (7), wherein it is preferable that the beam oscillationmeans uses an electro-optic effect. According to this configuration, thebeam oscillation means oscillates light not mechanically with the use ofa mechanism but electrically with the use of the electro-optic effect.Oscillation can be therefore performed at a high speed in a stablemanner.

(9) A 2-D image display is the 2-D image display device set forth in anyof (1) through (8), wherein it is preferable that the coherent lightsource is formed of a blue coherent light source, a green coherent lightsource, and a red coherent light source. According to thisconfiguration, light sources for respective RGB use coherent lightsources for monochromatic light having adequate wavelengths. It is thuspossible to achieve a 2-D image display device capable of displaying asharp color image having high color purity.

(10) A 2-D image display device is the 2-D image display device setforth in (9), wherein it is preferable that: the blue coherent lightsource and the red coherent light source are semiconductor laser lightsources; the green coherent light source is formed of the infraredcoherent light source and light wavelength conversion means forconverting a wavelength of light from the infrared coherent light sourceto half the wavelength; the display device further includes highfrequency current superimposing means for superimposing a high frequencycurrent on driving currents for the red coherent light source and theblue coherent light source; and the beam oscillation means is integratedinto a same substrate for the light wavelength conversion means.

According to this configuration, the high frequency currentsuperimposing means superimposes a high frequency current on drivingcurrents for the blue coherent light source and the red coherent lightsource, both of which are semiconductor lasers. Hence, the spectrumbandwidth of a laser beam emitted from the semiconductor laser expands,and the coherency is reduced. The speckle noises induced from scatteringon the screen can be therefore suppressed.

Also, in the green coherent light source, the wavelength of the lightfrom the red coherent light source is converted to half the wavelengthby the light wavelength conversion means. In this instance, the beamoscillation means for oscillating green coherent light is not formed asa separate mechanism component apart from the light modulationconversion means; instead, it is integrated into the same substrate forthe light wavelength conversion means. This can be achieved by, forexample, using lithium niobate, which is non-linear optical crystal, asthe substrate, and by forming both the light wavelength converting meansand the beam oscillation means in this substrate. As a result, thenumber of components can be reduced and the device can be more compact.When configured in this manner, it is possible to achieve a 2-D imagedisplay device capable of displaying a sharp color image in which thespeckle noises are suppressed.

(11) A 2-D image display device is the 2-D image display device setforth in (9), wherein it is preferable that: the red coherent lightsource is a semiconductor laser light source; the green coherent lightsource is formed of a first infrared coherent light source and lightwavelength conversion means for green for converting a wavelength oflight from the first infrared coherent light source to half thewavelength; the blue coherent light source is formed of a secondinfrared coherent light source and light wavelength conversion means forblue for converting a wavelength of light from the second infraredcoherent light source to half the wavelength; the display device furtherincludes high frequency current superimposing means for superimposing ahigh frequency current on a driving current for the red coherent lightsource; and the beam oscillation means is integrated into a samesubstrate for the light wavelength conversion means for green and into asame substrate for the light wavelength conversion means for blue.

According to this configuration, the high frequency currentsuperimposing means superimposes a high frequency current on a drivingcurrent for the red coherent light source, which is a semiconductorlaser. Hence, the spectrum bandwidth of a laser beam emitted from thesemiconductor laser expands, and the coherency is reduced. The specklenoises induced from scattering on the screen can be thereforesuppressed. Also, in the blue coherent light source and the greencoherent light source, the light wavelength conversion means convertsthe wavelength of light from the infrared coherent light source to halfthe wavelength. In other words, the wavelength of the first infraredcoherent light source provided to the green coherent light source istwice the wavelength of desired green, and the wavelength of the secondinfrared coherent light source provided to the blue coherent lightsource is twice the wavelength of desired blue.

Also, the beam oscillation means for oscillating blue or green coherentlight is not formed as a separate mechanism component apart from thelight modulation conversion means; instead, it is integrated into thesame substrate for the light wavelength conversion means. This can beachieved by, for example, using lithium niobate, which is non-linearoptical crystal, as the substrate, and by forming both the lightwavelength converting means and the beam oscillation means in thissubstrate. As a result, the number of components can be reduced and thedevice can be more compact. When configured in this manner, it ispossible to achieve a 2-D image display device capable of displaying asharp color image in which the speckle noises are suppressed.

(12) As has been described, an illumination light source according tothe invention of the present application preferably includes: a coherentlight source; beam scan means for scanning light from the coherent lightsource; light intensity modulation means for modulating the light fromthe coherent light source in intensity; and beam oscillation means forminutely oscillating the light from the coherent light source.

According to this configuration, light from the coherent light source ismodulated in intensity by the light intensity modulation means accordingto, for example, an input video signal, and projected onto a certainscreen or the like. In this instance, the beam scan means can beconfigured to scan the light either one-dimensionally ortwo-dimensionally. In the case of the configuration to scan the lightone-dimensionally, by providing a mechanism that scans the light in adirection orthogonal to the scan direction to the outside, it ispossible to display an image, for example, on a 2-D screen.

Also, the projected light is oscillated minutely by the beam oscillationmeans, and thereby irradiates different sites on the screensuccessively. The pattern of the speckle noises induced by scatteredlight therefore changes one after another as well. This allows thetime-mean pattern of the speckle noises to be perceived by human eyes.It is thus possible to achieve a light source that enables display of ahigh quality video in which are suppressed the speckle noises specificto a display device using a coherent light source, such as a laser lightsource.

While the invention has been described in detail, the description aboveis illustrative and not restrictive in all aspects. It is thereforeunderstood that a number of modifications that are not described hereincan be anticipated without deviating from the scope of the invention.

INDUSTRIAL APPLICABILITY

The 2-D image display device of the invention is able to display ahigh-quality image having no speckle noises, and is applicable to a TVreceiver, a projection-type data display, a home theater system, atheatrical movie projection device, and a large-screen advertisementdisplay medium. The invention is also applicable to a manufacturingdevice using the photolithography, such as an aligner for integratedcircuit manufacturing.

1-12. (canceled)
 13. A 2-D image display device comprising: a coherent light source; 2-D beam scan means for scanning light from the coherent light source two-dimensionally; light intensity modulation means for modulating the light from the coherent light source in intensity; and beam oscillation means for minutely oscillating the light from the coherent light source.
 14. The 2-D image display device according to claim 13, further comprising: beam collection means for collecting the light from the coherent light source onto a screen.
 15. The 2-D image display device according to claim 13, wherein: the beam oscillation means oscillates the light from the coherent light source in a direction perpendicular to a scan line by the 2-D beam scan means.
 16. The 2-D image display device according to claim 13, wherein: the beam oscillation means oscillates the light on the screen in amplitude equal to or larger than a spot diameter of the light collected on the screen by the beam collection means, and equal to or smaller than an interval of scan lines by the 2-D beam scan means.
 17. The 2-D image display device according to claim 13, wherein: while the 2-D beam scan means scans the light from the coherent light source comparable to one digital image data along a scan line, the beam oscillation means oscillates the light at least from largest amplitude to following largest amplitude.
 18. The 2-D image display device according to claim 13, wherein: while the 2-D beam scan means scans the light from the coherent light source comparable to one digital image data along a scan line, the beam oscillation means oscillates the light in a non-integral multiple of one cycle.
 19. The 2-D image display device according to claim 13, wherein: in a case where the light from the coherent light source is oscillated in N cycles by the beam oscillation means while the 2-D beam scan means scans the light from the coherent light source comparable to one digital image data along a scan line, a spot diameter of the light projected onto the screen is of a size equal to or larger than 1/(4N) of a distance over which the light is scanned by the 2-D beam scan means within the scan time.
 20. The 2-D image display device according to claim 13, wherein: the beam oscillation means uses an electro-optic effect.
 21. The 2-D image display device according to claim 13, wherein: the coherent light source is formed of a blue coherent light source, a green coherent light source, and a red coherent light source.
 22. The 2-D image display device according to claim 21, wherein: the blue coherent light source and the red coherent light source are semiconductor laser light sources; the green coherent light source is formed of an infrared coherent light source and light wavelength conversion means for converting a wavelength of light from the infrared coherent light source to half the wavelength; the display device further comprises high frequency current superimposing means for superimposing a high frequency current on driving currents for the red coherent light source and the blue coherent light source; and the beam oscillation means is integrated into a same substrate for the light wavelength conversion means.
 23. The 2-D image display device according to claim 21, wherein: the red coherent light source is a semiconductor laser light source; the green coherent light source is formed of a first infrared coherent light source and light wavelength conversion means for green for converting a wavelength of light from the first infrared coherent light source to half the wavelength; the blue coherent light source is formed of a second infrared coherent light source and light wavelength conversion means for blue for converting a wavelength of light from the second infrared coherent light source to half the wavelength; the display device further comprises high frequency current superimposing means for superimposing a high frequency current on a driving current for the red coherent light source; and the beam oscillation means is integrated into a same substrate for the light wavelength conversion means for green and into a same substrate for the light wavelength conversion means for blue.
 24. An illumination light source comprising: a coherent light source; beam scan means for scanning light from the coherent light source; light intensity modulation means for modulating the light from the coherent light source in intensity; and beam oscillation means for minutely oscillating the light from the coherent light source. 